The present invention concerns classification of particulate material in liquid dispersion by sedimentation so as to obtain at least two fractions of particulate material of different densities, and the recovery of at least one of such fractions. The sedimentation may be induced by gravity by centrifugation and the liquid dispersion to be classified in accordance with the present invention may be suspensions or emulsions.
The present invention is applicable to a variety of purposes such as diagnostic, analytical and preparative operations, typical applications being the separation of leucocytes from native blood, the splitting of a recovered leucocyte fraction into B-cells and T-cells, separation of an antigen/antibody complex produced in vitro in a reaction mixture from other particulate material, classification of lipoproteins, classification of marrow cells and the like.
For certain centrifugation techniques there are commonly used test tube-like vessels so designed that they are capable of withstanding the high stresses prevailing during centrifugation. In such a vessel the interface between layers resulting from centrifugation is a labile structure and consequently special care has to be taken in order to avoid back-mixing of the fractions. This in turn gives rise to problems in the separation of fractions from each other with the consequence that such separation is a tedious and slow operation.